The grammar is taken from the postgresql directory in the antlrv4 grammars repo.

All of the files in the /antlr directory are taken directly from the repo. After copying the files from the repo, python3 transformGrammar.py must be run from the root of the repo.

The string_stack.go, postgresql_parser_base.go, and postgresql_lexer_base.go are also copied from the grammars repo.

The go files can then be generated by running the following commands from the ./antlr directory:

antlr4 -Dlanguage=Go -o ../ ./PostgreSQLLexer.g4
antlr4 -Dlanguage=Go -o ../ ./PostgreSQLParser.g4